Composition and method for detection of molecules of interest

ABSTRACT

Compositions comprising electrospun fibers and colorimetric detection encapsulated thereto are provided. Further, methods of use of said composition, including, but not limited to in-situ detection of molecules of interest, such as explosive compounds, are provided.

RELATED APPLICATIONS

This application is continuation of U.S. application Ser. No. 15/311,889filed Nov. 17, 2016, which is a national stage application under 371 ofPCT/IL2015/050531 filed on May 19, 2015, and claims the benefit of ILpatent application number 232696 filed on May 19, 2014. The contents ofthe above applications are all incorporated by reference as if fully setforth herein in their entirety.

FIELD OF INVENTION

The present invention is directed to, inter alia, compositionscomprising electrospun nanofibers and colorimetric reactants. Theinvention is further directed to methods of use of said compositions fordetection of molecule of interest including but not limited toexplosives.

BACKGROUND OF THE INVENTION

Recent security regulations and army operational requirements demandon-site detection of explosives to enable rapid identification so thatswift action may be taken. Also, convenient methods for explosiveresidue collection and detection are desired for the analysis ofpre-detonated devices or large pieces of post-blast debris, for whichtransport to an off-site laboratory is neither possible nor practical.The colorimetric field detection kits that are used by army and securityforces around the world are based on reagents that dissolve in a liquidmedia and produce a colored compound when reacting with traces ofexplosives. However, liquid detection in a dynamic field environment isinconvenient, and potentially hazardous in case of spill and exposure toacidic solutions or fire. The majority of the dry detection methods thatare used today rely on spectrometric techniques such as ion mobilityspectrometry (IMS), analyzing either trace particles or vapor samples(J. Yinon and S. Zitrin, Modern Methods and Applications in Analysis ofExplosives, Wiley, 1996). In IMS detection, a wipe taken from acontaminated surface in the field can be analyzed directly, eliminatingsample preparation steps and thus increasing sample throughput. Althoughthe instruments are sufficiently sensitive, operating it under fieldconditions is cumbersome.

An efficient method for fabrication of nanofibers is electrospinning. Inthis method, a liquid, typically a polymer solution is introduced into astrong electrostatic field, where the charged solution is drawn out intoa jet. The jet then undergoes extensive stretching and thinning, with anextension rate on the order of 1000 s⁻¹, and rapid evaporation of thesolvent. Ultra-thin fibers, having diameters in the range of micrometersto tens of nanometers, are formed in milliseconds. The morphology of theelectrospun fibers is governed by several parameters such as the appliedvoltage, needle-to-collector distance, feed rate of solution,temperature, humidity, as well as the properties of the polymersolution, such as electrical conductivity, surface tension, viscosity,viscoelasticity, solvent volatility and chemical compatibility betweenthe polymer and the solvent. The high specific surface area ofnanofibers is valuable for many applications, among them particlecollection, filtration, sensors, wound dressing, tissue engineering anddrug delivery.

Methods for manufacturing electrospun elements as well as encapsulatingor attaching molecules thereto are disclosed, inter alia, in WO2014/006621, WO 2013/172788, WO 2012/014205, WO 2009/150644, WO2009/104176, WO 2009/104175, WO 2008/093341 and WO 2008/041183, to oneof the present inventors and co-workers, the contents of which are fullyincorporated herein by reference.

US Patent Application Publication No. 2012/0282705 provides explosivesdetection substrates which include an electrospun (electro)sprayedand/or dry spun aromatic polymer, such as polystyrene, and a smallmolecule fluorophore. Methods for detecting an explosive material arealso provided relying on the amount of fluorescence emitted by theexplosives detecting substrate.

US Patent Application Publication No. 2011/0086415 relates topre-concentrator compositions, devices, systems, and/or methods forconcentrating small quantities of chemical, biological, radioactive,nuclear and explosive agents (i.e., CBRNE compounds).

Recent publications reported tubular nanostructures for trace-leveldetection of explosives (Rui Li, et al. small 2012, 8, No. 2, 225-230;Ying Wang, et al. Adv. Funct. Mater. 2012, 22, 3547-3555; Shengyang Taoet al. J. Mater. Chem., 2007, 17, 2730-2736; Yufei Yang et al. J. Mater.Chem., 2011, 21, 11895-11900; Bowei Xu et al. Polym. Chem., 2013, 4,5056; Yuan-Yuan Lv et al. Sensors and Actuators B 184, 2013, 205-211;Gudrun Bunte et al. Analytica Chimica Acta 591, 2007, 49-56; Yunxia Xuet al. Materials Letters 87, 2012, 20-23). The detection methodsdescribed in these publications rely on vapor diffusion of the targetedexplosives and require fluorescence sensing such as by UV light foranalysis.

There exists a long-felt need for highly sensitive and selective meansof sampling contaminated surfaces and detecting molecules of interest,including but not limited to, explosive compounds, while maintainingsafety of the user and the subject under observation. The development ofinexpensive swabs capable of on-site detection of explosives, withoutthe need of an additional detection device, is therefore desirable.

SUMMARY OF THE INVENTION

The present invention provides, in some embodiments, compositions andkits comprising electrospun nanofibers and colorimetric reactantsencapsulated thereto. In some embodiments, the colorimetric reactantsprovide a colorimetric change in response to exposure to a molecule ofinterest, including but not limited to explosive compounds. The presentinvention further provides methods of preparation of said compositionsand methods for the detection of molecules of interest by applying saidcompositions to a surface.

According to a first aspect, there is provided a composition comprisingat least one type of electrospun nanofiber and at least one colorimetricreactant, the electrospun nanofiber comprises a shell and a core, saidcore comprises the at least one colorimetric reactant, and said shellhas a glass transition between 70° C. to 150° C. In some embodiments,said shell is configured to break upon normal stress of 0.08-1 kg/cm² ata temperature range of −55° C. to 60° C.

In another embodiment, said composition has a porosity span from 60% to95%. In another embodiment, said porosity comprises a plurality ofinterconnected tunnels within said composition. In another embodiment,the composition comprises pores having a pore size ranging from 0.1 to100 micrometer.

In another embodiment, the composition comprises a shell having athickness in the range of about 100 nm to about 5 micrometer. In anotherembodiment, the thickness of the shell is in the range of 0.1-1micrometer. In another embodiment, the composition comprises a corehaving a diameter in the range of about 50 nm to about 10 micrometer.

In another embodiment, the electrospun shell of said nanofiber comprisesa polymer selected from the group consisting of poly(methylmethacrylate-co-ethylacrylate) (PMCEA), poly (e-caprolactone)(PCL), fluoropolymer, tetrafluoroethylene, sulfonatedtetrafluoroethylene, polyamide, poly(siloxane), poly(silicone),poly(ethylene), poly(vinyl pyrrolidone), poly(-hydroxyethylmethacrylate), poly(N-vinyl pyrrolidone), poly(methylmethacrylate), poly(vinyl alcohol), poly(acrylic acid), poly(vinylacetate), polyacrylamide, poly(ethylene-co-vinyl acetate), poly(ethyleneglycol), poly(methacrylic acid), polylactide, polyglycolide,poly(lactide-coglycolide), polyanhydride, polyorthoester,poly(carbonate), poly(acrylonitrile), poly(ethylene oxide), polyaniline,polyvinyl carbazole, polystyrene, poly(vinyl phenol), polyhydroxyacid,poly(caprolactone), polyanhydride, polyhydroxyalkanoate, polyurethane,polysaccharide, or a combination thereof.

In another embodiment, the electrospun core of said nanofiber furthercomprises a polymer selected from the group consisting of, poly(acrylicacid), fluoropolymer, poly(vinyl acetate), polyacrylamide,poly(ethylene-co-vinyl acetate), poly(ethylene glycol), poly(methacrylicacid), polylactide polyglycolide, poly(lactide-coglycolide),polyanhydride, polyorthoester, poly(carbonate), poly(ethylene oxide),polyaniline, polyvinyl carbazole, polystyrene, poly(vinyl phenol),polyhydroxyacid, polysaccharide, or a combination thereof.

In another embodiment, the composition further comprises at least onepolymer compound. In one embodiment, said at least one polymericcompound provides a support (e.g., mechanical support) to saidcomposition. In another embodiment, said at least one polymer compoundis selected from the group consisting of poly (e-caprolactone) (PCL),fluoropolymer, polyamide, poly(siloxane), poly(silicone),poly(ethylene), poly(vinyl pyrrolidone), poly(-hydroxyethylmethacrylate), poly(N-vinyl pyrrolidone), poly(vinyl alcohol),poly(acrylic acid), poly(vinyl acetate), polyacrylamide,poly(ethylene-co-vinyl acetate), poly(ethylene glycol), poly(methacrylicacid), polylactide, polyglycolide, poly(lactide-coglycolide),polyanhydride, polyorthoester, poly(acrylonitrile), poly(ethyleneoxide), polyaniline, polyvinyl carbazole, poly(vinyl phenol),polyhydroxyacid, polyanhydride, polyhydroxyalkanoate, polyurethane, or acombination thereof.

In another embodiment, the composition comprises a plurality ofelectrospun nanofibers types and a plurality of colorimetric reactants,wherein each type of electrospun nanofiber comprises at least one typeof a colorimetric reactant. In another embodiment, said composition isconfigured to enable a sequence of chemical reactions.

In another embodiment, said at least one colorimetric reactant has a pHvalue of at most 6. In another embodiment, said at least onecolorimetric reactant has a pH value of at least 8. In anotherembodiment said at least one colorimetric reactant is reactive with atleast one compound selected from a nitro-based compound, aperoxide-based compound, a chlorate and a bromated. In anotherembodiment, said at least one colorimetric reactant is an explosivedetection reagent. In another embodiment, the explosive detectionreagent is selected from the group consisting of: a Meisenheimercomplex, a Griess reagent, a thymol reagent and a Nesslers reagent. Inanother embodiment, said composition is useful for detection of anexplosive substance.

According to another aspect, there is provided method for the detectionof a molecule of interest on a sample, the method comprising contacting(e.g., rubbing) the sample with the composition of the invention,wherein a colorimetric change within the composition indicates that thesample has at least trace amounts of the molecule of interest, therebydetecting a molecule of interest on said surface. In another embodiment,the molecule of interest is a hazardous substance. In anotherembodiment, the hazardous substance is an explosives substance. Inanother embodiment, said contacting is applying stress (e.g., normalstress) between said composition and said sample. In another embodiment,said stress is sufficient for breaking the electrospun shell. In anotherembodiment, said normal stress is of about 0.08-1 kg/cm². In anotherembodiment, said stress is sufficient for breaking the electrospunshell.

According to another aspect, there is provided kit for sampling anddetecting a molecule of interest, the kit comprises at least onecomposition of the invention and optionally a carrier for saidcomposition. In another embodiment, said carrier is selected from aglove and a stick. In another embodiment, said molecule of interest is ahazardous substance. In another embodiment, said hazardous substance isan explosive substance. In another embodiment, said kit is for samplingand detecting a plurality of molecules of interests, the kit comprises aplurality of compositions of the present invention, wherein eachcomposition independently comprises at least one colorimetric reactantfor detecting at least one molecules of interest.

Further embodiments and the full scope of applicability of the presentinvention will become apparent from the detailed description givenhereinafter. However, it should be understood that the detaileddescription and specific examples, while indicating preferredembodiments of the invention, are given by way of illustration only,since various changes and modifications within the spirit and scope ofthe invention will become apparent to those skilled in the art from thisdetailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1. 2,4,6-trinitrotoluene (TNT)-dicyclohexylamine (DCHA) chargetransfer complex formation.

FIG. 2. The Greiss reaction for nitrate detection.

FIG. 3: The oxidation mechanism of N-phenylanthranilic acid (NPA).

FIG. 4: The chlorate colorimetric detection.

FIG. 5: Coaxial-electrospinning of liquid cored and polymer shellednanofibers.

FIG. 6: Image of co-electrospun TNT detecting swab (left part of theimage), and after detection of 0.05 mg TNT (right part of the image).

FIGS. 7A-B. Cryo high-resolution scanning electron microscopy(Cryo-HR-SEM) images of (7A) The cross-sections of reinforced core/shellfibers, made from DCHA core and 350k PMCEA shell (core is in whitecolor) and (7B) The core/shell-PAN matrix.

FIGS. 8A-E. Optical mages of (8A) Co-electrospun mat and (8B) afterdetection of 0.05 mg TNT. SEM images of DCHA as a core in 101K PMCEAshell fibers: (8C) Hollow fibers after breakage, presenting a brittlefracture, where the DCHA (the dark color) released and stained thesubstrate; (8D) PMCEA fracture pattern along the fiber, and (8E) DCHAwhich was not properly encapsulated by the PMCEA shell.

FIG. 9. Ultraviolet-visible (UV-Vis) absorbance spectrum of the DCHA-TNTcomplex after addition of 100 μg TNT wiped over the swab (grey line) andafter being added to 3 ml of core solution (black line).

FIGS. 10A-C are images of the nitrate detecting swab, before (10A), andafter (10B) 5 second from detection of 10 μg ammonium nitrate (AN), andafter addition of one drop of water 10C).

FIG. 11. UV-Vis absorbance spectra of the nitrates swab after additionof 1 mg ammonium nitrate (AN), 5 seconds (--- striped line) and 5minutes (- continuous line) from AN addition.

FIG. 12. UV-Vis absorbance spectra of the chlorates swab after detectionof potassium chlorate (purple line) and ammonium nitrate (green line).

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides compositions comprising electrospunfibers and methods of use thereof for the detection of molecules ofinterest. In some embodiments, the electrospun fibers comprise a shelland a core comprising colorimetric reactants. In some embodiments, thecore of colorimetric reactants is encapsulated to the electrospun shell.

The present invention is based, in part, on detection of molecules ofinterest, including but not limited to an explosive substance, using wetchemistry analysis (i.e., chemistry performed substantially in theliquid phase). In another embodiment, the composition of the inventionprovides a reaction system in which at least one reaction is conductedin a solution. In another embodiment, the composition of the inventionprovides a reaction system in which a sequence of chemical reactions areconducted in a solution. As used herein, the term “a sequence ofchemical reactions” refers to at least two, at least three, at leastfour or at least five chemical reactions. One skilled in the art willappreciate that the unique features of the composition of the invention(e.g., compartmentalization of reagents in separate microfibers) enablesa reaction system in which a sequence of chemical reactions areconducted in a solution.

In another embodiment, the unique structure of the electrospunnanofibers described herein provides increased sampling and immediatedetection of molecules of interest at the solid or liquid state. Inanother embodiment, detection of molecules of interest is achievedaccording to the invention when said molecule is in a liquid phase or asolid phase. In another embodiment, the composition and methods of theinvention provide particulate detection of molecules of interest.

In another embodiment, the invention provides compositions and methodsenabling a one-step analysis of a surface suspected of having traceamounts of a molecule of interest, such as, explosives. Without wishingto be bound by any theory or mechanism of action, the unique structureof the electrospun nanofibers comprising a shell and a core comprisingor composed of colorimetric reactants encapsulated to the shell, whereinthe shell is configured to break upon stress (e.g., by shear stressand/or by swiping a surface being analyzed) exposes the colorimetricreactants to the surface leading to the occurrence of a chemicalreaction between the colorimetric reactants and molecules of interestupon the surface. In additional embodiments, the present inventionprovides a plurality of electrospun nanofiberes independently comprisingcolorimetric reactants, effective for performing a sequence of chemicalreactions.

According to some embodiments, the invention provides compositions forsampling and detecting molecules of interest, such as explosivecompounds, on surfaces for their subsequent immediate colorimetricdetection.

Colorimetric detection methods are a low-cost tool for assessing thenature and extent of contamination and enabling on-site screening. Theterm “colorimetric” is defined as an analysis where the reagent orreagents of the composition of the invention produce a color change inthe presence of an analyte, i.e., the molecule of interest.

In some embodiments, the composition of the invention may be in the formof a device, e.g., a swab. In some embodiments, the swab providessampling and detection in a single medium. In some embodiments, the swabprovides means for holding, protecting, and/or maintaining fibers of theinvention in a non-broken (whole) form. In some embodiments, the swab'sstructure provides a multi-scale assembly of nano scale fibers, microscale fibers, or a combination thereof. In another embodiment, themulti-scale assembly of the fibers within a swab creates an increasedsurface area. In some embodiments, the increased surface area of theswab enables enhanced collection efficiency of molecules of interest.

The device described herein, e.g., in a form of a swab, can be indifferent sizes depending on the type of surface to be sampled. Theshape of the swab can be, without limitation, circular, oval, square,rectangular, or any other shape suitable to purpose of the swab. Inanother embodiment, the swab is affixed to the end of a glove or aholder. The swab can be permanently or temporarily affixed to the gloveor holder for ease of manipulation, usage and sampling. In anotherembodiment, the swab is disposable. The swab may be used by military,law enforcement, homeland security, and others.

In another aspect, the present invention provides a gel encapsulatedswab. In some embodiments, said gel encapsulated swab comprises at leasttwo layers of electrospun fibers and a detecting paste (i.e., a layercomprising colorimetric reagent) between the at least two layers ofelectrospun fibers.

Explosives

In particular embodiments, the present invention provides compositionsand methods for detection of explosives molecules. In anotherembodiment, the colorimetric reactants encapsulated or attached to theelectrospun core are explosive-detection reagents.

As exemplified herein below, the compositions of the invention werehighly effective in sampling and detecting of 2,4,6-trinitrotoluene(TNT) and ammonium nitrate, using the TNT-DCHA charge transfer complexformation, or the Greiss three-step reaction, respectively. Anadditional composition was effective in sampling and detecting potassiumchlorate, using NPA oxidation.

In another embodiment, the compositions and methods of the invention areuseful for detection of settled explosive compounds. In anotherembodiment, the compositions and methods of the invention are useful fordetection of solid or liquid explosive compounds.

In some embodiments, the present invention provides a highly sensitivedetection composition. Accordingly, in some embodiments, the compositiondescribed herein is capable of detecting an explosive material in verysmall amounts. Sensitivity may be measured by the amount (in weight) ofexplosive material required to produce a colorimetric reaction with thereagents within the electrospun fiber. In some embodiments, thecomposition is capable of producing a colorimetric reaction in thepresence of an explosive material in an amount less than about 10 lessthan about 1 μg, less than about 500 ng, less than about 250 ng or lessthan about 100 ng. Each possibility represents a separate embodiment ofthe present invention.

The term “explosives”, as used herein is intended to encompass explosivecompounds, explosive byproducts as well as explosive precursors.According to some embodiments, the explosives are selected fromnitroaromatics, organic nitrates (also termed “nitroesters”),nitramines, inorganic nitrates, chlorates and bromates. Examples ofexplosive agents that may be detected by the methods and compositionsdescribed herein include but are not limited to, ammonium nitrate/fueloil (AN/FO), amatol, ammonium nitrate, ammonium picrate, dynamite,guanidine nitrate, gunpowder,octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX),hexanitrostilbene, lead azide, lead styphnate, mannitol hexanitrate,mercury fulminate, naphthacene, nitroguanidine, pentaerythritoltetranitrate (PETN), picric acid,hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), 1,3,5-trinitrobenzene(TNB), 1,3-dinitrobenzene (DNB), methyl-2,4,6-trinitrophenylnitramine(Tetryl), nitrobenzene (NB), 2,4,6-trinitrotoluene (TNT), picric acid(PA), 2,4-dinitrotoluene (24DNT), 2,6-dinitrotoluene (26DNT),o-nitrotoluene (2NT), m-nitrotoluene (3NT), p-nitrotoluene (4NT),nitroglycerin (NG), 4-amino-2,6-dinitrotoluene (4-Am-DNT),2-amino-4,6-dinitrotoluene (2-Am-DNT), pentaerythritol tetranitrate(PETN), 2,3-dimethyl-2,3-dinitrobutane (DMNB), acetone peroxide (TATP),triaminotrinitrobenzene (TATB) and tritonal. Each possibility representsa separate embodiment of the present invention.

In another embodiment, the colorimetric reactants are reactive withnitroaromatics, including but not limited to TNT, DNT and tetryl. Inanother embodiment, the colorimetric reactants are reactive withnitramines or nitrate esters including but not limited to RDX, HMX,PETN, EGDN and NG. In another embodiment, the colorimetric reactants arereactive with inorganic nitrates including but not limited to ureanitrate, ammonium nitrate and black powder. In another embodiment, thecolorimetric reactants are reactive with chlorate and/or bromatesincluding but not limited to potassium chlorate and potassium bromated.In another embodiment, the colorimetric reactants are reactive withperoxides e.g. TATP and HMTD. In another embodiment, the colorimetricreactants are reactive with acids e.g. nitric acid, sulfuric acid andcitric acid. In another embodiment, the colorimetric reactants arereactive with bases e.g. potassium hydroxide and sodium hydroxide

TNT Colorimetric Detection:

TNT colorimetric detection typically relies on the Meisenheimer reaction(J. Meisenheimer, “Ueber Reactionen aromatischer Nitrokörper,” JustusLiebigs Ann. Chem. 323 (2), 205 (1902)) to create a chromophore from thenitroaromatic explosive molecule and a hydroxyl ion (OH—). In someembodiments, a Meisenheimer Complex solution is used as a colorimetricreactant of the invention. Typically, tetrabutylammonium hydroxide inethanol gives a color indication for TNT, tetryl, and trinitrobenzene.

According to another embodiment, the colorimetric detection is based oncymantrene (cyclopentadienyl manganesetricarbonyl), which exhibits acolor change when it comes into contact with several nitroaromatics,under UV radiation (S. J. Toal and W. C. Trogler, J. Mater. Chem. 16,2871, 2006; L. M. Dorozhkin, et al., Sensors and Actuators B 99, 568,2004).

In another embodiment, a dicyclohexylamine (DCHA) based colorimetricreactant is used. DCHA based colorimetric detector is known in the artfor detection of TNT and Tetryl (2,4,6-trinitrophenyl-N-methylnitramine)(A. Uzer, et al. 2004, Anal. Chim. Acta 505, 83; A. Uzer, et al. 2009,Talanta 78, 772). Its detection is based on intermolecularcharge-transfer (CT) between the electron-attracting nitroaromatics andelectron-donating amine, DCHA (FIG. 1), resulting in a deep violet colorand UV-Vis absorbance. The CT between primary amines and explosives wasmay also be used for the detection of explosive species, using nanowiresensor arrays without any further chemical treatment (Y. Engel, 2010, etal. Angew. Chem. Int. Ed. 49, 6830).

Nitrate Colorimetric Detection:

In some embodiments, a Griess reaction is used for colorimetricdetection of nitrate. The Griess three-step reaction is known in the artas the standard nitrate colorimetric detection method (J. P. Griess,Philos. Trans. R. SOC. London, 164, 683, 1864) as presented in FIG. 2.In this reaction, the nitrate is first reduced to nitrite, which thenreacts to conjugate a sulfanilic acid to an aromatic amine and producesan azo dye product, having a deep violet color and a 540 nm visiblelight absorbance.

Chlorate Colorimetric Detection:

In some embodiments, N-phenylanthranilic acid (NPA) is used forcolorimetric detection of chlorates. As known in the art NPA oxidationresults in two detection colored products: (1) green (λmax=430 nm) and(2) violet (λmax=550 nm); depending on the oxidant's nature, aspresented in FIG. 3, (K. Sriramam, Talanta, 20, 383, 1973). In thepresence of NPA (FIG. 4), the colorimetric reaction for chlorates isimmediate, giving a deep violet colored product; whereas thecolorimetric reaction of other strong oxidizers is delayed, resulting ina pale colored product compared to chlorate.

In some embodiments, the methods of the present teachings allow for thedetection of explosive materials on surfaces such as hands, clothing,cars, packages, luggage, door handles, buildings, land, desks,computers, and more.

In another embodiment, the at least one colorimetric reactant of thecomposition of the invention has a pH value of at most 6. In anotherembodiment, said at least one colorimetric reactant has a pH value of atleast 8. In another embodiment said at least one colorimetric reactantis reactive with at least one compound selected from a nitro-basedcompound, a peroxide-based compound, a chlorate and a bromated. Inanother embodiment, said at least one colorimetric reactant is anexplosive detection reagent. In another embodiment, the explosivedetection reagent is selected from the group consisting of: aMeisenheimer complex, a Griess reagent, a thymol reagent and a Nesslersreagent. In another embodiment, said composition is useful for detectionof an explosive sub stance.

In some embodiments, molecules that may be detected by the methods andcompositions of the disclosure include toxic or chemical agents, andpollutants, such as but not limited to, Tabun, Sarin, Soman, VX,mustard, lewisite, phosgene, chlorine, ammonia, cyanide, Mace®, pepperspray, nerve agents, vesicants, industrial chemicals, and riot controlagents.

Electrospun Fibers

According to some embodiments, the compositions of the inventioncomprise at least one type of electrospun nanofiber and at least onecolorimetric reactant encapsulated therein. In some embodiments, theelectrospun nanofiber comprises a shell and a core, wherein the corecomprises or is composed of the at least one colorimetric reactant.

According to another embodiment, the fibers of the invention are nothollow or of a tubular shape, but are composed of a brittle (or fragile)shell and a core of colorimetric reactant(s). In another embodiment, theshell is substantially filled with the colorimetric core. As usedherein, a brittle shell refers to a shell configured to break uponstress, thereby exposing (or releasing) the core's colorimetricreactants.

In another embodiment, the shell has a glass transition of at least 50°C., at least 55° C., at least 60° C., at least 65° C., at least 70° C.,at least 75° C., or at least 80° C. In another embodiment, the shell hasa glass transition of at least 70° C. In another embodiment, the shellhas a glass transition of at most 150° C., at most 145° C., at most 140°C., at most 135° C., at most 130° C., at most 125° C., or at most 120°C. In another embodiment, the shell has a glass transition of at most150° C.

“Tg” or “glass transition temperature” of a polymer is the temperatureat which a polymer transitions from a rigid, glassy state attemperatures below its Tg to a fluid or rubbery state at temperaturesabove Tg. The Tg of a polymer is measured by differential scanningcalorimetry (DSC) using the mid-point in the heat flow versustemperature transition as the Tg value.

As used herein, the term “configured to break upon stress” included butis not limited to normal stress, shear stress, or a combination ofnormal stress and shear stress, as such as developed upon swiping asurface being analyzed. In some embodiments, said shell is configured tobreak upon normal stress of at least 0.08, at least 0.09, at least 0.1,at least 0.15, at least 0.2, at least 0.25, at least 0.3, at least 0.35,at least 0.4, at least 0.45 or at least 0.5 kg/cm′ at a temperaturerange of −55° C. to 60° C. In some embodiments, said shell is configuredto break upon normal stress of at most 0.6, at most 0.65, at most 0.7,at most 0.75, at most 0.8, at most 0.85, at most 0.9, at most 0.95 or atmost 1 kg/cm² at a temperature range of −55° C. to 60° C. “Normalstress” is defined herein as the stress acting perpendicular to asurface.

In some embodiments, the core is a liquid core. In another embodiment,the shell is i.e., is at a state of liquid. In another embodiment, saidshell has a low porosity and diffusion for preventing leakage of thecore (e.g., a liquid core) encapsulated within the shell. In someembodiments, said shell has a low porosity and diffusion in the order ofabout 10⁻¹⁰ (cm² s-¹), or any other order as determined by a skilledartisan, according to the core's state.

In another embodiment, said composition has a porosity span of at least30%, at least 35%, at least 40%, at least 45%, at least 50%, at least55%, at least 60%, at least 65%, at least 70%, at least 75%, at least80%, at least 85%, at least 90% or at least 95%. In another embodiment,said porosity comprises a plurality of interconnected tunnels withinsaid composition. In another embodiment, the composition comprises poreshaving a pore size ranging from 0.1 to 100 micrometer.

In another embodiment, the composition comprises a plurality ofelectrospun nanofibers types and plurality colorimetric reactants,wherein each type of electrospun nanofiber comprises at least one typeof a colorimetric reactant. In another embodiment, said composition isconfigured to enable a sequence of chemical reactions.

The term “electrospun” or “(electro)sprayed” when used in reference topolymers are recognized by persons of ordinary skill in the art andincludes fibers produced by the respective processes. Such processes aredescribed in more detail infra.

Methods for manufacturing electrospun elements as well as encapsulatingor attaching molecules thereto are disclosed, inter alia, in WO2014/006621, WO 2013/172788, WO 2012/014205, WO 2009/150644, WO2009/104176, WO 2009/104175, WO 2008/093341 and WO 2008/041183, all toone of the present inventors and co-workers, the contents of which arefully incorporated herein by reference.

Manufacturing of electrospun elements can be done by an electrospinningprocess which is well known in the art. Following is a non-limitingdescription of an electrospinning process. One or more liquefiedpolymers (i.e., a polymer in a liquid form such as a melted or dissolvedpolymer) are dispensed from a dispenser within an electrostatic field ina direction of a rotating collector. The dispenser can be, for example,a syringe with a metal needle or a bath provided with one or morecapillary apertures from which the liquefied polymer(s) can be extruded,e.g., under the action of hydrostatic pressure, mechanical pressure, airpressure and high voltage.

The rotating collector (e.g., a drum) serves for collecting theelectrospun element thereupon. Typically, but not obligatorily, thecollector has a cylindrical shape. The dispenser (e.g., a syringe withmetallic needle) is typically connected to a source of high voltage,preferably of positive polarity, while the collector is grounded, thusforming an electrostatic field between the dispenser and the collector.Alternatively, the dispenser can be grounded while the collector isconnected to a source of high voltage, preferably with negativepolarity. As will be appreciated by one ordinarily skilled in the art,any of the above configurations establishes motion of positively chargedjet from the dispenser to the collector. Inverse electrostaticconfigurations for establishing motions of negatively charged jet fromthe dispenser to the collector are also contemplated.

At a critical voltage, the charge repulsion begins to overcome thesurface tension of the liquid drop. The charged jets depart from thedispenser and travel within the electrostatic field towards thecollector. Moving with high velocity in the inter-electrode space, thejet stretches and solvent therein evaporates, thus forming fibers whichare collected on the collector, thus forming the electrospun element.

As used herein, the phrase “electrospun element” refers to an element ofany shape including, without limitation, a planar shape and a tubularshape, made of one or more non-woven polymer fiber(s), produced by aprocess of electrospinning. When the electrospun element is made of asingle fiber, the fiber is folded thereupon, hence can be viewed as aplurality of connected fibers. It is to be understood that a moredetailed reference to a plurality of fibers is not intended to limit thescope of the present invention to such particular case. Thus, unlessotherwise defined, any reference herein to a “plurality of fibers”applies also to a single fiber and vice versa. In some embodiments, theelectrospun element is an electrospun fiber, such as electrospunnanofiber. As used herein the phrase “electrospun fiber” relates to afibers formed by the process of electro spinning.

The electrospun fibers of the invention comprise an electrospun shelland a core. As used herein, the phrase “electrospun shell” refers to anelement of a tubular shape, made of one or more polymers, produced bythe process of electrospinning. As used herein the phrase “core” refersto an internal layer within the electrospun shell, which is made of atleast one colorimetric reactant, and optionally one or more polymers. Inanother embodiment, the core is encapsulated within the electrospunshell. In some embodiments, the core is an electrospun core, i.e.,prepared by the process of electrospinning. In some embodiments, thefiber's core is not in a solid state. In some embodiments, the fiber'score is in a liquid state. In some embodiments wherein the fiber's coreis in a liquid state, said shell has low porosity, as such as to preventdiffusion or leakage of the liquid core.

One of ordinary skill in the art will know how to distinguish anelectrospun object from objects made by means which do not compriseelectrospinning by the high orientation of the macromolecules, the shellmorphology, and the typical dimensions of the fibers which are unique toelectrospinning.

According to some embodiments of the invention the thickness of theelectrospun shell of the invention can vary from a few nanometers toseveral micrometers, such as from about 100 nm to about 20 μm(micrometer), e.g., from about 200 nm to about 10 μm, from about 100 nmto about 5 μm, from about 100 nm to about 1 μm, e.g., about 500 nm. Inanother embodiment, the composition comprises a core having a diameterin the range of about 50 nm to about 10 micrometer.

According to some embodiments of the invention, the electrospun fibermay have a length which is from about 0.1 millimeter (mm) to about 20centimeter (cm), e.g., from about 1-20 cm, e.g., from about 1-10 cm.According to some embodiments of the invention, the length (L) of theelectrospun fibers of some embodiments of the invention can be severalorders of magnitude higher (e.g., 10 times, 100 times, 1000 times,10,000 times, e.g., 50,000 times) than the fiber's diameter (D).

According to some embodiments of the invention, the electrospun fiber isproduced by a method which comprises co-electrospinning two solutionsthrough co-axial capillaries, wherein a first solution of the twosolutions is for forming a shell of the fiber and a second solution ofthe two solutions is for forming a core within the shell. In someembodiments, said solution is a polymeric solution.

As used herein the phrase “co-electrospinning” refers to a process inwhich at least two solutions are electrospun from co-axial capillaries(i.e., at least two capillary dispensers wherein one capillary is placedwithin the other capillary while sharing a co-axial orientation) formingthe spinneret within an electrostatic field in a direction of acollector. The capillary can be, for example, a syringe with a metalneedle or a bath provided with one or more capillary apertures fromwhich the solution can be extruded, e.g., under the action ofhydrostatic pressure, mechanical pressure, air pressure and/or highvoltage.

For forming a core/shell structure by electro spinning, a first solutionis injected into the outer capillary of the co-axial capillaries while asecond solution (also referred herein as a core solution) is injectedinto the inner capillary of the co-axial capillaries. In someembodiments wherein the core is not a liquid core, the first solution(which is for forming the shell/sheath of the fiber) solidifies fasterthan the core solution. In some embodiments, the formation of core/shellstructure also requires that the solvent of the core solution beincapable of dissolving the first solution. The solidification rates ofthe first and second solutions are critical for forming a core/shellfiber. As a non-limiting example of a core/shell fiber of about 100 μmwherein the core is not a liquid core, the solidification of the firstsolution can be within about 30 milliseconds (ms) while thesolidification of the core polymer, if occurs, can be within about 10-20seconds. The solidification may be a result of polymerization rateand/or evaporation rate.

According to some embodiments of the invention, the solvent of thepolymeric solution evaporates faster than the solvent of second solution(e.g., the solvent of the first solution exhibits a higher vaporpressure than the solvent of the second solution). In one embodiment,the shell solidifies and the core remains in a liquid form. In oneembodiment, the shell solidifies faster than the core.

The flow rates of the first and second solutions can determine thefibers outer and inner diameter and thickness of shell. Non-limitingexamples are shown in Table 1 and Table 2 herein below.

In some embodiments, said first solution, said second solution (i.e.,the core solution), or both are a polymeric solution. As used herein thephrase “polymeric solution” refers to a soluble polymer, i.e., a liquidmedium containing one or more polymers, co-polymers or blends ofpolymers dissolved in a solvent. The polymer used by the invention canbe a natural, synthetic, biocompatible and/or biodegradable polymer.

The phrase “synthetic polymer” refers to polymers that are not found innature. Examples include, but are not limited to, aliphatic polyesters,poly(amino acids), copoly(ether-esters), polyalkylenes, oxalates,polyamides, tyrosine derived polycarbonates, poly(iminocarbonates),polyorthoesters, polyoxaesters, polyamidoesters, polyoxaesterscontaining amine groups, poly(anhydrides), polyphosphazenes, andcombinations thereof. Further examples include: fluoropolymerpolyethylene, polyethylene terephthalate, poly(tetrafluoroethylene),polycarbonate, polypropylene and poly(vinyl alcohol), and combinationsthereof.

Laboratory equipment for electrospinning can include, for example, aspinneret (e.g. a syringe needle) connected to a high-voltage (5 to 50kV) direct current power supply, a syringe pump, and a groundedcollector. A solution such as a polymer solution, sol-gel, particulatesuspension or melt is loaded into the syringe and this liquid isextruded from the needle tip at a constant rate (e.g. by a syringepump).

In another embodiment, the electrospun shell of said compositioncomprises a polymer selected from the group consisting of poly(methylmethacrylate-co-ethylacrylate) (PMCEA), poly (e-caprolactone)(PCL), fluoropolymer, tetrafluoroethylene, sulfonatedtetrafluoroethylene, polyamide, poly(siloxane), poly(silicone),poly(ethylene), poly(vinyl pyrrolidone), poly(-hydroxyethylmethacrylate), poly(N-vinyl pyrrolidone), poly(methylmethacrylate), poly(vinyl alcohol), poly(acrylic acid), poly(vinylacetate), polyacrylamide, poly(ethylene-co-vinyl acetate), poly(ethyleneglycol), poly(methacrylic acid), polylactide, polyglycolide,poly(lactide-coglycolide), polyanhydride, polyorthoester,poly(carbonate), poly(acrylonitrile), poly(ethylene oxide), polyaniline,polyvinyl carbazole, polystyrene, poly(vinyl phenol), polyhydroxyacid,poly(caprolactone), polyanhydride, polyhydroxyalkanoate, polyurethane,polysaccharide, or a combination thereof.

In another embodiment, the electrospun core of said composition furthercomprises a polymer selected from the group consisting of, poly(acrylicacid), fluoropolymer, poly(vinyl acetate), polyacrylamide,poly(ethylene-co-vinyl acetate), poly(ethylene glycol), poly(methacrylicacid), polylactide polyglycolide, poly(lactide-coglycolide),polyanhydride, polyorthoester, poly(carbonate), poly(ethylene oxide),polyaniline, polyvinyl carbazole, polystyrene, poly(vinyl phenol),polyhydroxyacid, polysaccharide, or a combination thereof.

In another embodiment, said electrospun shell comprises poly(methylmethacrylate-co-ethylacrylate) (PMCEA). In another embodiment,the composition comprises 10% PMCEA in ethylacetate (EA) as a shellsolution, and 10% dicyclohexylamine (DCHA) in N-Methyl-2-pyrrolidone(NMP), Triethanolamine (TEA) (1:3 by weight) as a core solution.

In another embodiment, the composition comprises 10% PMCEA in EA as ashell solution and a plurality of core solutions, wherein a first coresolution comprises 10 wt. % sulfanilic acid and 10 wt. %sodium-carbonate in H2O, a second core solution comprises 25 wt. %naphthyl-ethylenediamine 2HCl in N-Methyl-2-pyrrolidone (NMP), a thirdcore solution comprises 50 wt. % tartaric acid in H2O, and a forth coresolution comprises 5 wt. % zinc dust in glycerin.

In another embodiment, the composition further comprises 20 wt. % Nylon6,6 (polyamide, PA) in formic acid (FA): trifluoroethanol (TFE) (7:3 byweight).

In another embodiment, the composition further comprises at least onepolymer compound. In one embodiment, said at least one polymericcompound provides a support (e.g., mechanical support) to saidcomposition. In another embodiment, said at least one polymer compoundis selected from the group consisting of poly (e-caprolactone) (PCL),fluoropolymer, tetrafluoroethylene, sulfonated tetrafluoroethylene,polyamide, poly(siloxane), poly(silicone), poly(ethylene), poly(vinylpyrrolidone), poly(-hydroxy ethylmethacrylate), poly(N-vinylpyrrolidone), poly(vinyl alcohol), poly(acrylic acid), poly(vinylacetate), polyacrylamide, poly(ethylene-co-vinyl acetate), poly(ethyleneglycol), poly(methacrylic acid), polylactide, polyglycolide,poly(lactide-coglycolide), polyanhydride, polyorthoester,poly(acrylonitrile), poly(ethylene oxide), polyaniline, polyvinylcarbazole, poly(vinyl phenol), polyhydroxyacid, polyanhydride,polyhydroxyalkanoate, polyurethane, or a combination thereof.

In some embodiments, parameters of the electrospinning process mayaffect the resultant substrate (e.g. the thickness, porosity, etc.).Such parameters may include, for example, molecular weight, molecularweight distribution and architecture (branched, linear etc.) of thepolymer, solution properties (viscosity, conductivity & and surfacetension), electric potential, flow rate, concentration, distance betweenthe capillary and collection screen, ambient parameters (temperature,humidity and air velocity in the chamber) and the motion and speed ofthe grounded collector. Accordingly, in some embodiments, the method ofproducing a substrate as described herein includes adjusting one or moreof these parameters.

In the discussion unless otherwise stated, adjectives such as“substantially” and “about” modifying a condition or relationshipcharacteristic of a feature or features of an embodiment of theinvention, are understood to mean that the condition or characteristicis defined to within tolerances that are acceptable for operation of theembodiment for an application for which it is intended. Unless otherwiseindicated, the word “or” in the specification and claims is consideredto be the inclusive “or” rather than the exclusive or, and indicates atleast one of, or any combination of items it conjoins.

In the description and claims of the present application, each of theverbs, “comprise,” “include” and “have” and conjugates thereof, are usedto indicate that the object or objects of the verb are not necessarily acomplete listing of components, elements or parts of the subject orsubjects of the verb.

Additional objects, advantages, and novel features of the presentinvention will become apparent to one ordinarily skilled in the art uponexamination of the following examples, which are not intended to belimiting. Additionally, each of the various embodiments and aspects ofthe present invention as delineated hereinabove and as claimed in theclaims section below finds experimental support in the followingexamples.

EXAMPLES Materials and Methods

All materials were used as is: Rilsan Polyamide (PA, Arkema); Formicacid (FA) (99% LOBA Chemie); Trifluoroethanol (TFE) (99%,Sigma-Aldrich); Dicyclohexylamine (DCHA) (99%, Sigma-Aldrich);Triethanolamine (TEA) (99%, Merck); N-Methyl-2-pyrrolidone (NMP) (99.5%,Merck); Poly (methylmethacrylate-co-ethylacrylate) (PMCEA) (Mw-101k and350k gr/mol, Sigma-Aldrich); Ethylacetate (EA) (99%, Frutarom);Polyacrylonitrile (PAN) (Mw-150k gr/mol, Sigma-Aldrich);Dimethylforamide (DMF) (99.8%, Frutarom); Sulfanilic acid (99%,Sigma-Aldrich); Sodium carbonate (99%, Sigma-Aldrich);Naphthyl-ethylenediamine-dihydrochloride (98%, Sigma-Aldrich); Zinc dust(<10 μm, 98%, Sigma-Aldrich); Glycerine oil (99%, Frutarom);Dimethylsulfoxide (DMSO) (99%, Merck); Poly(vinylidenefluoride-co-hexafluoropropylene)) (PVDF-HFP) (Mw-400k gr/mol,Sigma-Aldrich); Tetrahydrofuran (THF) (99%, Frutarom); p-toluenesulfonicacid monohydrate (98.5%, Sigma-Aldrich); N-phenylanthranilic acid (98%,Merck); Distilled water.

Electrospinning Fibers

The co-electrospinning set up is shown in FIG. 5 and the productionconditions are detailed in Table 1. A double spinneret was designed toallow for the delivery of two different liquid solutions simultaneouslyinto a coaxial capillary, under high voltage (10 kV) between thespinneret and a grounded collector. When subjecting the polymer to ahigh electrostatic field (-1 kV/cm), a compound Taylor cone, composed oftwo coaxial cones, is formed at the tip of the spinneret. By selectingthe process conditions (e.g., applied voltage, solutions feed rates) andadjusting the material properties of the polymer solutions (e.g.,solution viscosities, solvent-solution miscibility, solutionconcentration, and solvent vapor pressure), a continuous single jetcontaining the two solution flows is extracted electrically out of theconverging point of the Taylor cone.

Images and Spectroscopy

SEM Images were taken using a PHENOM scanning electron microscope (FEICompany), and a Zeiss ultra-plus cryogenic high resolution scanningelectron microscope (cryo-HRSEM), equipped with a BAF-060 cryogenicetching chamber. Light microscope images were taken at ×115 zoom, usinga SZX16 Fluorescent Binocular light microscope (Olympus), equipped withSuper Depth of Focus (SDF) objective lenses, which reaches a 0.3numerical aperture (NA) and a 900 lp/mm resolution, illuminated by anultra-slim 40 mm LED base. Imaging of the wipe materials was taken,using a Nikon D90 DSLR camera equipped with a compatible G-type AF-SMicro-Nikkor lens having a focal length of 105 mm and a maximum apertureof f/2.8. Exposures were carried out with a lens to sample distance ofca. 40 cm. shutter speed of ⅕ sec and aperture of f/4.5. Opticalabsorbance scans were conducted using a GENESYS 10 UV-Vis scanningspectrophotometer (335906 Thermo Scientific equipped with a Xenon lamp).Absorbance was scanned over the range of 300-700 nm, at 1 nm/secinterval. Liquid samples were measured in quartz cuvettes and fibersamples were mounted on a designated holder. The level of detection wasquantified by measuring the detection coverage (area where a colorchange is seen as result of the reaction) on the surface of the swab wasdone with Paint.Net©.

Example 1 TNT Detection and Characterization

In this work, the inventors of the present invention exemplified theconcept of sampling and detecting molecules of interests usingelectrospun microfibers. The exemplified molecules of interest included:a) bulk materials- of 2,4,6-trinitrotoluene (TNT), b) ammonium nitrate(AN), and c) potassium chlorate (chlorate), using the TNT-DCHA chargetransfer complex formation, the Greiss 3-step reaction and NPAoxidation, respectively. As will be described hereinbelow, the detectingreagents are encapsulated in nano-scale fibers. Upon fracture of a matof fibers during swiping, micro-gram quantities of the core reagentcould be delivered onto the nanofiber surface, and reach sampledmolecules of interest (e.g., explosive particles) for their subsequentdetection.

Encapsulation of the reagents was carried in two methods: (1) co-axialelectrospinning which enables the fabrication of a non-woven mat ofnano-fiber. The shell of the fiber is made ofPoly(methylmethacrylate-co-ethylacrylate) (PMCEA) characterized by ahigh Tg, allowing it to break down at room temperature under swipingpressure, exposing the encapsulated reagents to the explosives forvisual detection. (2) Spreading the reagent to be detectable between twolayers of electrospun fibers, resulting in a gel encapsulated swab.Examples of immediate visual colorimetric detection of explosives atmicrogram level are demonstrated.

TABLE 1 swab processing parameters of the TNT detecting swab Flow-Needle rate, material/ Distance, Voltage, ml/h O.D., gauge cm kV 1Stainless 20 40 Substrate: steel/25 G 20 wt. % Nylon 6,6 (PA) in 7:3 wt.% FA:TFE 5 Polypropylene/ 17 17 Shell solution: 17 G 10 wt. % 350k PMCEAin EA 5 Stainless 17 — Core Solution steel/21 G #1: 10% DCHA in 1:3 wt.% NMP:TEA 0.25 Stainless 17 17 Additional steel/21 G syringe: 8 wt. %PAN in DMF

FIG. 6 shows an image of the swab immediately after swiping a quantityof 5 μg TNT from a contaminated ABS surface, which produced an immediateviolet colored charge transfer complex (FIG. 1). The swab was mountedover a 5 mm diameter knob, and swiped 3 times at 0.4 kg force over 15 mmlength of the contaminated ABS surface. FIG. 7 shows cryo-HR-SEM imagesof the reinforced core/shell-PAN network that was used for the swipingexperiments.

FIG. 8 shows images of the co-electrospun mat after 0.1 mg TNTcontamination and photographed within seconds, with an Olympus SZX16Fluorescent Binocular light microscope. The high contrast between thewhite fibers and the colored TNT detected fibers is noticed. We can seethat the color effect is displayed along the fibers, where the core wasencapsulated.

FIG. 9 shows the UV-Vis absorbance spectrum of the DCHA-TNT complexafter the addition of 100 μg TNT: dispersed over a swab (grey line) andadded to 3 ml of core solution (black line). As a result of theCT-complex formation, two peaks are observed at 505 and 535 nm,consisting with typical DCHA-TNT absorbance spectrum (Uzer, et al.,2004, Anal. Chim. Acta 505, 83; and Uzer, et al., 2009, Talanta 78,772).

The TEA core solvent amine-moieties also couples to TNT to form aCT-complex. The TEA-TNT complexation result in delayed absorbance at 540nm, due to low electron donor activity of TEA, compared to DCHA.However, the high TEA concentration in the core solution compensates forits low donor activity and increases the total absorbance in the visibleregion. A third absorbance peak that was obtained at 460 nm in both theswab and the core solution spectrum, is suggested to represent themoisture influence on the CT spectra in alkaline solutions, resulting ina typical absorbance of the Meisenheimer complex. (Meisenheimer, JustusLiebigs Ann. Chem. 1902, 323 (2), 205). The 460 nm peak intensity wasmoisture dependent, and had almost no effect when the core solution wassealed off from air moisture, however, when swab handling and measuringtook place in the open lab air, moisture had a greater influence. Inspite of its competition with the charge transfer color reaction, themoisture effect increased the swab's absorbance intensity in the visibleregion and contributed to the rapid detection of TNT.

Example 2 Nitrates Detection and Characterization

Detection of nitrates under the Greiss reaction requires a sequence ofchemical reactions using zinc dust, tartaric acid, sulfanilic acid andnaphthyl-ethylenediamine-dihydrochloride. Due to the limited solubilityof all the four reactants of the nitrate detecting reaction in onesolvent, each of the components is dissolved separately and electrospunor electrosprayed as a separate layer on the nitrate detecting swab. Inthis method, we were able to increase the amount of each one of thecomponents, independently in the other ingredients. Upon swiping, thefragile shell breaks down, allowing all four components to combine andto react with nitrate contamination, and give an immediate violetdetecting color on the swab's surface. The layers structures of thenitrate detecting swab are detailed in Table 2. Since the nitratesdetection reaction is moisture sensitive, a drop of distilled water wasdrop over the swab post detection, in order to enhance the colorimetricyield.

Due to its high oxidative nature, most of the colorimetric tests forchlorates are performed in a liquid acidic medium, which may influencethe swab and packaging stability once introduced to a solid product. Toovercome this issue, we have used p-toluenesulfonic acid, which is asolid, non-corrosive, non-toxic acid, as a proton source for chloratecolorimetric detection.

FIG. 10 (a-c) show images of the reinforced nitrates detection swab,after swiping a quantity of 10 μg ammonium nitrate from a contaminatedABS surface, and dropping one drop of distilled water over the swab,which enhanced the violet color over the swab.

TABLE 2 Nitrate detecting swab- layers structure Flow- Needle rate,material/ Distance, Voltage, ml/h O.D., gauge cm kV 1 Stainless 20 40Substrate: steel/25 G 20 wt. % Nylon 6,6 in 7:3 wt. % FA:TFE 4Polypropylene/ 17 17 Shell solution: 17 G 10 wt. % 350k PMCEA in EA 2Stainless 17 — Core Solution steel/19 G #1: 10 wt. % Sulfanilic acid 10wt. % Sodium- carbonate in H₂O 2 Stainless 17 — Core Solution steel/21 G#2:25 wt. % Naphthyl - ethylene- diamine·2HCl in NMP 2 Stainless 17 —Core Solution steel/21 G #3: 50 wt. % Tartaric acid in H₂O 0.25Stainless 17 17 Additional steel/21 G syringe: 8 wt. % PAN in DMF 2Stainless 10 10 Electrospraying steel/21 G solution: 5 wt. % Zinc dustin Glycerin Processing Swab materials and quantity method Layer#Substrate: Nylon 6,6 -0.3 g Electrospinning 1 Core: sulfanilic acid-Core/shell 2 0.5 g , sodium carbonate- 0.5 g electrospinning Shell:PMCEA- 1 g Zinc dust- 0.2 g Electrospraying 3 in Glycerin- 4 g Core:Core/shell 4 naphthyl-ethylenediamine- electrospinning dihydrochloride-0.5 g Shell: PMCEA- 0.4 g Core: tartaric acid- 2 g Core/shell 5 Shell:PMCEA- 0.8 g electrospinning Zinc dust- 0.05 g Electrospraying 6 inGlycerin- 1 g Polyacrylonitrile- 0.11 g Simultaneously 2-6Electrospinning with layer 2 to 6.

FIG. 11 presents the UV-Vis absorbance spectra of the dye that wasproduced on the nitrates detecting swab, after detecting 10 μg AN, in 5seconds (continuous line), and 5 minutes (dashed line) from AN addition,without the addition of water. The absorbance peak at 540 nm matcheswith the expected literature reported absorbance of the violet azo-dyethat is produced in this reaction. The absorbance at 540 nm isincreasing gradually with time (continuous and dashed lines), indicatingthat the reaction continues until reaching a steady state, when theentire swab is covered in the violet typical azo-dye color.

Example 3 Chlorates Detection and Characterization

Poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) nanofibersubstrate showed the highest chemical resistance to p-toluenesulfonicacid during production and aging. Its hydrophobic fluorocarbon backboneresists water molecules from reaching to the hygroscopicp-toluenesulfonic acid and releasing protons. Nylon 6,6 (Polyamide, PA,)and polyacrylonitrile (PAN) however, did not withstand the high acidicconditions and their nanofibers were corroded during fabrication andaging.

TABLE 3 Chlorates detecting processing conditions Volt- Dis- NeedleFlow- age, tance, material/ rate, Time, kV cm O.D., gauge ml/h hoursSubstrate: 12 10 Stainless 3 3 15 wt. % steel/25 G PVDF-HFP in 50:50 wt.% THF:DMF 10 g of p-toluenesulfonic acid + 1 g of NPA were mixed at 40%humidity to a paste, spread over the substrate polymer fibrous layer,and covered with an additional thin PVDF-HFP fibrous layer, to givegel-encapsulated swabs.

FIG. 20 presents the UV-vis absorbance spectra of the dye that wasproduced on the chlorates detecting swab, after the detection ofpotassium chlorate (1 second), and ammonium nitrate (5 minutes). On-swabnitrates detection resulted in a khaki green colored product (λmax≈430nm), and chlorates detection resulted in a deep violet colored product(λmax≈550 nm). These results consist with literature, indicating on theweaker oxidation nature of the ammonium nitrate compared to thepotassium chlorate, resulting in a different product.

While the present invention has been particularly described, personsskilled in the art will appreciate that many variations andmodifications can be made. Therefore, the invention is not to beconstrued as restricted to the particularly described embodiments, andthe scope and concept of the invention will be more readily understoodby reference to the claims, which follow.

1. A swab comprising at least one type of electrospun nanofibers and atleast one colorimetric reactant, the electrospun nanofibers comprise abrittle shell and a core, said core comprises the at least onecolorimetric reactant, and said brittle shell has a glass transitionbetween 70° C. and 150° C. and is configured to break under normalstress of 0.08-1 kg/cm² at a temperature between −55° C. and 60° C., soas to allow detection of an analyte on a surface.
 2. The swab of claim1, wherein said brittle shell has a porosity span from 60% to 95%. 3.The swab of claim 1, wherein said brittle shell has a pore size rangingfrom 0.1 to 100 micrometer.
 4. The swab of claim 1, wherein said brittleshell has a thickness in the range of about 100 nm to about 5micrometer.
 5. The swab of claim 1, wherein said core has a diameter inthe range of about 50 nm to about 10 micrometer.
 6. The swab of claim 1,wherein said brittle shell is formed by electrospinning a firstpolymeric solution comprising (i) a polymer selected from the groupconsisting of poly (methylmethacrylate-co-ethylacrylate) (PMCEA),tetrafluoroethylene, sulfonated tetrafluoroethylene, poly(siloxane),poly(silicone), poly(vinyl pyrrolidone), poly(2-hydroxyethylmethacrylate), poly(N-vinyl pyrrolidone), poly(methylmethacrylate), poly(vinyl alcohol), poly(acrylic acid), polyacrylamide,poly(ethylene-co-vinyl acetate), polylactide, polyglycolide,polyanhydride, polyorthoester, poly(carbonate), poly(acrylonitrile),polyaniline, polystyrene, poly(vinyl phenol), polyhydroxyacid,polyhydroxyalkanoate, polysaccharide, or a combination thereof; (ii)optionally an additional polymer selected from the group consisting offluoropolymer, polyamide, poly(ethylene), poly(vinyl acetate),poly(ethylene glycol), poly(methacrylic acid),poly(lactide-coglycolide), poly(ethylene oxide), polyvinyl carbazole,poly(caprolactone), polyurethane, or a combination thereof.
 7. The swabof claim 1, wherein said brittle shell comprises poly(methylmethacrylate-co-ethylacrylate) (PMCEA).
 8. The swab of claim 1,wherein said core is formed by electrospinning a second polymericsolution comprising a polymer selected from the group consisting ofpoly(acrylic acid), fluoropolymer, poly(vinyl acetate), polyacrylamide,poly(ethylene-co-vinyl acetate), poly(ethylene glycol), poly(methacrylicacid), polylactide polyglycolide, poly(lactide-coglycolide),polyanhydride, polyorthoester, poly(carbonate), poly(ethylene oxide),polyaniline, polyvinyl carbazole, polystyrene, poly(vinyl phenol),polyhydroxyacid, polysaccharide, or a combination thereof.
 9. The swabof claim 1, comprising: (i) a plurality of electrospun nanofibers types;(ii) a plurality of colorimetric reactants; or (iii) both, wherein eachtype of electrospun nanofiber comprises at least one type of acolorimetric reactant reactive with at least one compound selected froma nitro-based compound, a peroxide-based compound, a chlorate and abromate.
 10. The swab of claim 1, wherein said at least one colorimetricreactant has a pH value selected from: (i) a pH value of at most 6; or(ii) a pH value of at least
 8. 11. The swab of claim 1, wherein said atleast one colorimetric reactant is reactive with at least one compoundselected from a nitro-based compound, a peroxide-based compound, achlorate and a bromate or any combination thereof.
 12. The swab of claim1, wherein said at least one colorimetric reactant is an explosivedetection reagent.
 13. The swab of claim 12, wherein the explosivedetection reagent is selected from the group consisting of: aMeisenheimer complex, a Griess reagent, a thymol reagent and a Nesslersreagent or any combination thereof.
 14. The swab of claim 1, furthercomprising at least one polymer compound for providing a mechanicalsupport to said swab.
 15. The swab of claim 14, wherein said at leastone polymer compound is selected from the group consisting ofpoly(e-caprolactone) (PCL), fluoropolymer, polyamide, poly(siloxane),poly(silicone), poly(ethylene), poly(vinyl pyrrolidone), poly(2-hydroxyethylmethacrylate), poly(N-vinyl pyrrolidone), poly(vinyl alcohol),poly(acrylic acid), poly(vinyl acetate), polyacrylamide,poly(ethylene-co-vinyl acetate), poly(ethylene glycol), poly(methacrylicacid), polylactide, polyglycolide, poly(lactide-coglycolide),polyanhydride, polyorthoester, poly(acrylonitrile), poly(ethyleneoxide), polyaniline, polyvinyl carbazole, poly(vinyl phenol),polyhydroxyacid, polyhydroxyalkanoate, polyurethane, or a combinationthereof.